1. Field of the Invention
The subject invention is directed to devices for measuring pressure, especially high pressures, and temperatures in a hydraulic or pneumatic system. More specifically, the subject invention concerns devices that incorporate both a piezo-resistive pressure measuring cell and an electronic circuit in one housing to form an integral component.
2. Description of the Prior Art
The usual types of manometers known in the prior art are generally read off only at intervals. Furthermore, such devices are frequently inadequate with regard to the precision required for certain measurements. In contrast, electronic measuring devices afford a continuous recording of the measured values and a rapid processing of the signals with a high degree of measuring accuracy.
Hydraulic systems are becoming increasingly complicated in the course of the rapid technical development. One consequence of this is that the hydraulic systems are placing increasingly higher demands on the required accuracy and switching speed of associated systems. As a result, there is a demand for improved pressure and temperature measuring devices that will not only continuously indicate the actual values measured by the electronic circuit, but will also give an instantaneous or real-time indication, of interference in the installation.
In piezo-resistive pressure measuring cells known in the prior art, the piezo-resistive semiconductor element (silicium chip) that is used for recording the pressure is connected to the corresponding contacts by means of binding wires. Thus, the entire sensor housing is standardized from semiconductor technology and is similar to that used for transistors, operational amplifiers, and the like. Consequently, such prior art sensor housing are unsuitable for measuring high pressures because the pressure influence on the housing distorts the measurement. Moreover, the housing often cannot withstand the higher pressures that are to be measured such that it is subject to deformation.
Pressure sensors are subject to thermal drift. This can be compensated for by measuring the temperature and adjusting the pressure sensor in accordance with the temperature changes. However, it is very important to adjust the pressure sensor on a continuous basis, particularly if the temperature changes are rapid.
In known hydraulic or pneumatic systems where pressure is monitored, the temperature is measured remotely from the pressure measurement. The pressure sensor is adjusted for temperature according to discrete units of temperature. This process creates errors; first because the temperature is not measured at the same time and location as the measurement of pressure, and second because rapid fluctuations of the remotely measured temperature induce a phase lag. Furthermore, the discrete temperature units permit only an approximate adjustment of the pressure sensor.
Thus, there was a need in the prior art for a device that would measure high pressure and temperature simultaneously to substantially improve the measurement accuracy through continuous temperature compensation.
There was also a need in the prior art for a measuring device that would provide a precise measurement that can readily be connected and assembled to hydraulic or pneumatic systems under high pressure.